Improvements to the Grid list demo (#3315)

* Improvements to the Grid list demo

* More nits and fixes to grid demo in gallery

examples/material_gallery/lib/demo/grid_list_demo.dart

@@ -3,11 +3,42 @@
 // found in the LICENSE file.
 
 import 'dart:collection';
-import 'dart:math' as math;
 
 import 'package:flutter/material.dart';
 import 'package:flutter/widgets.dart';
 
+import '../gallery/demo.dart';
+
+const String _kExampleCode =
+"""// Creates a scrollable grid list with images
+// loaded from the web.
+new ScrollableGrid(
+  delegate: new FixedColumnCountGridDelegate(
+    columnCount: 3,
+    tileAspectRatio: 1.0,
+    padding: const EdgeInsets.all(4.0),
+    columnSpacing: 4.0,
+    rowSpacing: 4.0
+  ),
+  children: <String>[
+    'https://example.com/image-0.jpg',
+    'https://example.com/image-1.jpg',
+    'https://example.com/image-2.jpg',
+    ...
+    'https://example.com/image-n.jpg'
+  ].map((String url) {
+    return new GridTile(
+      footer: new GridTileBar(
+        title: new Text(url)
+      ),
+      child: new NetworkImage(
+        src: url,
+        fit: ImageFit.cover
+      )
+    );
+  })
+);""";
+
 enum GridDemoTileStyle {
   imageOnly,
   oneLine,
@@ -15,89 +46,36 @@ enum GridDemoTileStyle {
 }
 
 class Photo {
-  const Photo({ this.assetName, this.title, this.caption });
+  Photo({ this.assetName, this.title, this.caption, this.isFavorite: false });
 
   final String assetName;
-
   final String title;
   final String caption;
 
-  bool get isValid => assetName != null;
-}
+  bool isFavorite;
 
-final List<Photo> photos = <Photo>[
-  const Photo(
-    assetName: 'packages/flutter_gallery_assets/landscape_0.jpg',
-    title: 'Philippines',
-    caption: 'Batad rice terraces'
-  ),
-  const Photo(
-    assetName: 'packages/flutter_gallery_assets/landscape_1.jpg',
-    title: 'Italy',
-    caption: 'Ceresole Reale'
-  ),
-  const Photo(
-    assetName: 'packages/flutter_gallery_assets/landscape_2.jpg',
-    title: 'Somewhere',
-    caption: 'Beautiful mountains'
-  ),
-  const Photo(
-    assetName: 'packages/flutter_gallery_assets/landscape_3.jpg',
-    title: 'A place',
-    caption: 'Beautiful hills'
-  ),
-  const Photo(
-    assetName: 'packages/flutter_gallery_assets/landscape_4.jpg',
-    title: 'New Zealand',
-    caption: 'View from the van'
-  ),
-  const Photo(
-    assetName: 'packages/flutter_gallery_assets/landscape_5.jpg',
-    title: 'Autumn',
-    caption: 'The golden season'
-  ),
-  const Photo(
-    assetName: 'packages/flutter_gallery_assets/landscape_6.jpg',
-    title: 'Germany',
-    caption: 'Englischer Garten'
-  ),
-  const Photo(assetName:
-    'packages/flutter_gallery_assets/landscape_7.jpg',
-    title: 'A country',
-    caption: 'Grass fields'
-  ),
-  const Photo(
-    assetName: 'packages/flutter_gallery_assets/landscape_8.jpg',
-    title: 'Mountain country',
-    caption: 'River forest'
-  ),
-  const Photo(
-    assetName: 'packages/flutter_gallery_assets/landscape_9.jpg',
-    title: 'Alpine place',
-    caption: 'Green hills'
-  ),
-  const Photo(
-    assetName: 'packages/flutter_gallery_assets/landscape_10.jpg',
-    title: 'Desert land',
-    caption: 'Blue skies'
-  ),
-  const Photo(
-    assetName: 'packages/flutter_gallery_assets/landscape_11.jpg',
-    title: 'Narnia',
-    caption: 'Rocks and rivers'
-  ),
-];
+  bool get isValid => assetName != null && title != null && caption != null && isFavorite != null;
+}
 
 const String photoHeroTag = 'Photo';
 
+typedef void PhotoFavoriteCallback(Photo photo);
+
 class GridDemoPhotoItem extends StatelessWidget {
-  GridDemoPhotoItem({ Key key, this.photo, this.tileStyle }) : super(key: key) {
+  GridDemoPhotoItem({
+    Key key,
+    this.photo,
+    this.tileStyle,
+    this.onPressedFavorite
+  }) : super(key: key) {
     assert(photo != null && photo.isValid);
     assert(tileStyle != null);
+    assert(onPressedFavorite != null);
   }
 
   final Photo photo;
   final GridDemoTileStyle tileStyle;
+  final PhotoFavoriteCallback onPressedFavorite;
 
   void showPhoto(BuildContext context) {
     Key photoKey = new Key(photo.assetName);
@@ -141,6 +119,8 @@ class GridDemoPhotoItem extends StatelessWidget {
       )
     );
 
+    IconData icon = photo.isFavorite ? Icons.star : Icons.star_border;
+
     switch(tileStyle) {
       case GridDemoTileStyle.imageOnly:
         return image;
@@ -148,8 +128,12 @@ class GridDemoPhotoItem extends StatelessWidget {
       case GridDemoTileStyle.oneLine:
         return new GridTile(
           header: new GridTileBar(
-            backgroundColor: Colors.black.withAlpha(0x08),
-            leading: new Icon(icon: Icons.info, color: Colors.white70),
+            backgroundColor: Colors.black45,
+            leading: new IconButton(
+              icon: icon,
+              color: Colors.white,
+              onPressed: () { onPressedFavorite(photo); }
+            ),
             title: new Text(photo.title)
           ),
           child: image
@@ -158,10 +142,14 @@ class GridDemoPhotoItem extends StatelessWidget {
       case GridDemoTileStyle.twoLine:
         return new GridTile(
           footer: new GridTileBar(
-            backgroundColor: Colors.black.withAlpha(0x08),
+            backgroundColor: Colors.black45,
             title: new Text(photo.title),
             subtitle: new Text(photo.caption),
-            trailing: new Icon(icon: Icons.info, color: Colors.white70)
+            trailing: new IconButton(
+              icon: icon,
+              color: Colors.white,
+              onPressed: () { onPressedFavorite(photo); }
+            )
           ),
           child: image
         );
@@ -169,46 +157,6 @@ class GridDemoPhotoItem extends StatelessWidget {
   }
 }
 
-class GridListDemoGridDelegate extends FixedColumnCountGridDelegate {
-  GridListDemoGridDelegate({
-    this.columnCount,
-    double columnSpacing: 0.0,
-    double rowSpacing: 0.0,
-    EdgeInsets padding: EdgeInsets.zero,
-    this.tileHeightFactor: 2.75
-  }) : super(columnSpacing: columnSpacing, rowSpacing: rowSpacing, padding: padding) {
-    assert(columnCount != null && columnCount >= 0);
-    assert(tileHeightFactor != null && tileHeightFactor > 0.0);
-  }
-
-  @override
-  final int columnCount;
-
-  final double tileHeightFactor;
-
-  @override
-  GridSpecification getGridSpecification(BoxConstraints constraints, int childCount) {
-    assert(constraints.maxWidth < double.INFINITY);
-    assert(constraints.maxHeight < double.INFINITY);
-    return new GridSpecification.fromRegularTiles(
-      tileWidth: math.max(0.0, constraints.maxWidth - padding.horizontal + columnSpacing) / columnCount,
-      tileHeight: constraints.maxHeight / tileHeightFactor,
-      columnCount: columnCount,
-      rowCount: (childCount / columnCount).ceil(),
-      columnSpacing: columnSpacing,
-      rowSpacing: rowSpacing,
-      padding: padding
-    );
-  }
-
-  @override
-  bool shouldRelayout(GridListDemoGridDelegate oldDelegate) {
-    return columnCount != oldDelegate.columnCount
-        || tileHeightFactor != oldDelegate.tileHeightFactor
-        || super.shouldRelayout(oldDelegate);
-  }
-}
-
 class GridListDemo extends StatefulWidget {
   GridListDemo({ Key key }) : super(key: key);
 
@@ -219,6 +167,69 @@ class GridListDemo extends StatefulWidget {
 class GridListDemoState extends State<GridListDemo> {
   GridDemoTileStyle tileStyle = GridDemoTileStyle.twoLine;
 
+  List<Photo> photos = <Photo>[
+    new Photo(
+      assetName: 'packages/flutter_gallery_assets/landscape_0.jpg',
+      title: 'Philippines',
+      caption: 'Batad rice terraces'
+    ),
+    new Photo(
+      assetName: 'packages/flutter_gallery_assets/landscape_1.jpg',
+      title: 'Italy',
+      caption: 'Ceresole Reale'
+    ),
+    new Photo(
+      assetName: 'packages/flutter_gallery_assets/landscape_2.jpg',
+      title: 'Somewhere',
+      caption: 'Beautiful mountains'
+    ),
+    new Photo(
+      assetName: 'packages/flutter_gallery_assets/landscape_3.jpg',
+      title: 'A place',
+      caption: 'Beautiful hills'
+    ),
+    new Photo(
+      assetName: 'packages/flutter_gallery_assets/landscape_4.jpg',
+      title: 'New Zealand',
+      caption: 'View from the van'
+    ),
+    new Photo(
+      assetName: 'packages/flutter_gallery_assets/landscape_5.jpg',
+      title: 'Autumn',
+      caption: 'The golden season'
+    ),
+    new Photo(
+      assetName: 'packages/flutter_gallery_assets/landscape_6.jpg',
+      title: 'Germany',
+      caption: 'Englischer Garten'
+    ),
+    new Photo(
+      assetName: 'packages/flutter_gallery_assets/landscape_7.jpg',
+      title: 'A country',
+      caption: 'Grass fields'
+    ),
+    new Photo(
+      assetName: 'packages/flutter_gallery_assets/landscape_8.jpg',
+      title: 'Mountain country',
+      caption: 'River forest'
+    ),
+    new Photo(
+      assetName: 'packages/flutter_gallery_assets/landscape_9.jpg',
+      title: 'Alpine place',
+      caption: 'Green hills'
+    ),
+    new Photo(
+      assetName: 'packages/flutter_gallery_assets/landscape_10.jpg',
+      title: 'Desert land',
+      caption: 'Blue skies'
+    ),
+    new Photo(
+      assetName: 'packages/flutter_gallery_assets/landscape_11.jpg',
+      title: 'Narnia',
+      caption: 'Rocks and rivers'
+    ),
+  ];
+
   void showTileStyleMenu(BuildContext context) {
     final List<PopupMenuItem<GridDemoTileStyle>> items = <PopupMenuItem<GridDemoTileStyle>>[
       new PopupMenuItem<GridDemoTileStyle>(
@@ -265,18 +276,34 @@ class GridListDemoState extends State<GridListDemo> {
           )
         ]
       ),
-      body: new ScrollableGrid(
-        delegate: new GridListDemoGridDelegate(
-          columnCount: (orientation == Orientation.portrait) ? 2 : 3,
-          rowSpacing: 4.0,
-          columnSpacing: 4.0,
-          padding: const EdgeInsets.all(4.0),
-          tileHeightFactor: (orientation == Orientation.portrait) ? 2.75 : 1.75
-        ),
-        children: photos.map((Photo photo) {
-          return new GridDemoPhotoItem(photo: photo, tileStyle: tileStyle);
-        })
-        .toList()
+      body: new Column(
+        children: <Widget>[
+          new Flexible(
+            child: new ScrollableGrid(
+              delegate: new FixedColumnCountGridDelegate(
+                columnCount: (orientation == Orientation.portrait) ? 2 : 3,
+                rowSpacing: 4.0,
+                columnSpacing: 4.0,
+                padding: const EdgeInsets.all(4.0),
+                tileAspectRatio: (orientation == Orientation.portrait) ? 1.0 : 1.3
+              ),
+              children: photos.map((Photo photo) {
+                return new GridDemoPhotoItem(
+                  photo: photo,
+                  tileStyle: tileStyle,
+                  onPressedFavorite: (Photo photo) {
+                    setState(() {
+                      photo.isFavorite = !photo.isFavorite;
+                    });
+                  }
+                );
+              })
+            )
+          ),
+          new DemoBottomBar(
+            exampleCode: _kExampleCode
+          )
+        ]
       )
     );
   }